This invention relates to a pneumatic tire which reduces a noise during driving resulting from a tread pattern (or a so-called "pattern noise").
Comfort to drive, particularly low noise, are required for a radial tire for a passenger car for high speed driving. A tread pattern of such a pneumatic tire uses a block pattern as a basic tread pattern. In other words, a plurality of main grooves extending in a tire circumferential direction are so disposed on the tread surface of the tire as to define a plurality of rib lines, and a plurality of lug grooves are provided to these rib lines so as to define blocks.
In conventional pneumatic tires having a tread pattern using the block pattern described above as the basic pattern, means for reducing the noise has been proposed which changes variably the number of blocks for each rib line and a predetermined number of blocks are disposed on the periphery of the tire as a repeating unit so that a frequency band of a pattern noise corresponding to the revolution of the tire is made different from one rib line to another.
In the conventional pneumatic tires described above, the angles of the lug grooves are constant, or the angle change is irregular or non-uniform, although the number of blocks is changed variably. Accordingly, the frequency bands of the pattern noise are not sufficiently dispersed, and for this reason, the noise occurs during driving and provides an offensive feeling to a driver.